1. Field of the Invention
The present invention is in the field of filling receivers with granular material and more particularly in the field of filling charcoal adsorber filters with granular charcoal. Specifically, the present invention relates to methods for filling a filter with granular charcoal, from above the filter, in a fashion to achieve a substantially uniform packing density of granular charcoal within the filter. The methods are designed to be used in conjunction with vertically oriented adsorber filter cells, to achieve uniform packing density within such cells, thereby avoiding channeling effects.
2. Description of the Prior Art
Apparatus for dispensing granular materials and for filling containers with granular materials have long been known and a variety of such apparatus has been used to perform these tasks. Typical of these devices are the apparatus shown in U.S. Pat. Nos. 117,718, 335,709 and 2,511,089.
With evolving technology, the need has arisen for more sophisticated apparatus and for methods for packing granular material in a substantially uniform fashion within a hopper, filter or other structure. This requirement is particularly acute in air filter systems which use adsorbers for filtering radioactive materials from the air at a nuclear power plant.
The United States Nuclear Regulatory Commission has issued Regulatory Guides which set forth general design criteria for the design of nuclear power plants and the allied equipment required therefor. One key system for nuclear power plant is an atmospheric clean-up system for which general design guidelines are given in NRC Regulatory Guide 1.52. As an integral part of the atmospheric clean-up system at least one adsorption unit is required for adsorbing radioactive materials from the air after an accident. Adsorption units are manufactured in a variety of configurations, one of which is described in pending U. S. Pat. No. 3,964,890. Another configuration is shown in U.S. Pat. No. 3,925,046. These units require the adsorber filter to be filled with adsorbent material, preferably charcoal, from above the unit and that filling result in a substantially uniform density of adsorbent within the adsorber filter. This prevents "channeling" whereby paths of low resistance are available for air passing through the adsorber unit. Channeling is undesirable since air, to be properly filtered, must spend sufficient time in residence in the adsorber cell so that radioactive waste in the air can be adsorbed by charcoal. Cells with channeling do not produce satisfactory residence time for air passing therethrough and consequently the air is not sufficiently purified.
In the past, it was thought that by vibrating an adsorber unit filled with granular charcoal, charcoal settling would occur thereby minimizing channeling. In fact, vibration of a filled cell of the adsorber apparatus may result in aggravating the channeling problem due to vibrational nodes in the cell structure with consequent non-uniform vibration of the adsorber unit and charcoal therein.
Experiments have shown that the methods of the present invention not only provide a uniform packing density of charcoal adsorbent when utilized to fill a charcoal adsorber cell, but also acheive greater packing density than achieved by vibrating the cell. Such greater packing density enhances cell performance and has a further advantage in that by increasing flow resistance through the adsorber cell, flow irregularity, due to possible entrance and exit effects where air enters and leaves the cell, is also decreased. Most importantly, the methods produce very uniform packing of a charcoal adsorber cell. This results in uniform flow resistance to air passing through the cell.